In the modern world, technology is everywhere. At any given time, a person probably has in their field of view an object that was manufactured at a factory. Computers, cell phones, cars, and even to a large extent the food many people eat has been part of a lengthy production line. Many things are required to produce the finished products we see today, such as manpower and infrastructure, but possibly the most important piece of modern production is power. Many different types of machines are utilized in the manufacturing and packaging of a product, and they all require mechanical work to accomplish their goal. Some machines are entirely mechanical, such as a simple steam engine, but in the modern world most machines depend on electrical components and power to achieve optimal functioning as well. Electrical power is also integral to virtually all aspects of life in developed countries, with applications from refrigerating food to operating televisions, computers, radios, and other appliances, to operating traffic signals, among many others.
Electricity generation is the process of generating electric energy from other forms of energy. The fundamental principle of electricity generation is known as Faraday's law, and it can be used to generate electricity by the movement of a loop of wire or disc of copper between the poles of a magnet. This method of converting mechanical energy into electricity can be utilized in a number of different ways, including utilizing falling water or human power to turn a turbine, using a combustion engine to turn a crank, or using a heat source to power an engine, such as with a type of engine known as a Stirling engine.
In the modern world, it is desirable to discover and develop clean, renewable sources of energy. Of particular interest to many is the harnessing of naturally occurring energy sources. If the energy is there already in one form or another such as motion or radiation, constructing apparatuses to convert such energy into electricity is essentially generating free power, aside from the construction, maintenance and operational costs, since the resource used to generate the power is not one that can be purchased. One such energy source is hydroelectric power, which harnesses the natural motion of water, such as an ocean current or a waterfall, to generate electricity. Another, similar source of “free” energy is wind power. Yet another widely considered option for renewable energy is solar power, which harnesses the energy in sunlight to produce electrical power. Many solar power generation installations utilize photovoltaic technology to convert sunlight into electricity, while others utilize concentrated solar power to provide a heat source for a conventional power plant. One such application utilizes a Stirling engine.
A Stirling engine is a heat engine that operates by cyclic compression and expansion of a working fluid at different temperature levels so that there is a net conversion of heat energy to mechanical work. The Stirling engine is traditionally classified as an external combustion engine like the steam engine since all heat transfers occur through a solid boundary. This contrasts with an internal combustion engine where heat input is by combustion of a fuel within the body of the working fluid. Typical of heat engines, the general cycle consists of compressing cool gas, heating the gas, expanding the hot gas, and finally cooling the gas before repeating the cycle. The efficiency of the process is narrowly restricted by the efficiency of the Carnot cycle, which depends on the temperature difference between the hot and cold reservoir. Advantages of the Stirling engine are that it is highly efficient compared to steam engines, its operation is relatively quiet, and it can easily use almost any heat source. This compatibility with alternative and renewable energy sources has become increasingly significant as the price of conventional fuels rises, and also in light of concerns such as peak oil and climate change.
Current Stirling engine designs are subject to cracking of the heater tubes and external regenerator due to high thermal stress. In addition, pumping losses are high. Designing Stirling engine heat exchangers is a balance between high heat transfer with low viscous pumping losses and low dead space, or unswept internal volume. By eliminating the heater tubes, the heat transfer process is more directly associated with the working gas as it dwells in the heater head. By adding an internal regenerator to the displacer piston, the working fluid is utilized more efficiently and unswept volume is reduced. In addition, stresses in the heater head and regenerator assembly are reduced, allowing high temperature ceramics to be utilized, which significantly increases the efficiency of the engine because the efficiency is dependent on the difference in temperature between the hot and cold sections.
In a Stirling engine, the regenerator is an internal heat exchanger and provides temporary heat storage between the hot and cold spaces such that the working fluid passes through it first in one direction and then the other. Its function is to retain heat within the system that would otherwise be exchanged with the environment at temperatures intermediate to the maximum and minimum temperatures, increasing the thermal efficiency of the engine by recycling internal heat which would otherwise be lost.
One application well suited to the present invention is in waste heat recovery. The present invention may use waste heat from other mechanical, electrical or other devices such as another generator or a peak shaver which would otherwise be discarding useful heat energy. Ideally, the present invention would be used for waste heat recovery in continuously running applications.
It is therefore an object of the present invention to provide a Stirling engine displacer piston with an internal regenerator and integral geometry for more efficient heat transfer and fluid flow, ultimately resulting in a more highly efficient Stirling engine.